Abstract

Amorphoustungsten oxide exhibits electrochromism when intercalated with protons, lithium, sodium, and other ions. Thin films of the material were prepared by dc magnetron sputtering and then electrochemically intercalated with lithium. The optical absorption in the wavelength range of was measured for a number of lithium concentrations. The optical absorption shows a maximum for lithium/tungsten ratios of 0.3–0.5. The optical spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between , , and sites. The variation of the peak strength with lithium concentration is consistent with an extended site-saturation theory.

Received 16 June 2007Accepted 30 August 2007Published online 25 October 2007

Acknowledgments:

This work was supported by a grant from the Swedish Science Council (VR). We are grateful for valuable discussions with C. G. Granqvist. We also want to thank J. Backholm for help with computer software.